fiber.

I always read a product's nutrition label to see two things: the amount of fiber and the ingredients.  I usually will not eat a product that has less then 2 grams of fiber per serving (with the exception of Greek yogurt, of course). Why?  Because fiber helps control weight gain, prevents constipation, hemorrhoids, diverticulosis, certain cancers and type 2 diabetes, and lowers LDL cholesterol (the bad kind).  Fiber is the portion of the plant that cannot be digested by the gastrointestinal tract.  Therefore, it is not metabolized into energy.  Fiber can be found in two different forms, insoluble and soluble.

Insoluble Fiber:  Passes through our intestines largely intact.  Speeds up intestinal transit time and controls the pH of our intestines. Food sources of insoluble fiber include whole grain products (i.e. popcorn, whole grain bread), wheat and corn bran, nuts, seeds, fruit skins, dark green leafy vegetables. 

Soluble Fiber: Forms a gel when mixed with liquids.  Delays intestinal transit time (sugar is released more slowly into the bloodstream) and decreases the level of cholesterol in the blood by binding with fatty acids.  Food sources of soluble fiber include oats, legumes, oranges, apples, carrots, and barley. 

The average American consumes 14-15 grams of fiber per day (as per the Academy of Nutrition and Dietetics).   That is half of the daily recommendation of 20-35 grams.  Start aiming for 25 grams of fiber per day by increasing consumption of high fiber foods slowly.  Sneaking in fiber can be easy by using whole wheat flour when baking, whole grain bread with your PB&J, adding fresh fruit to your cereal, tossing some beans into your salad and swapping brown rice for white rice and whole wheat pasta for white pasta.  But remember, when increasing fiber, do it slowly and also increase water intake (this will prevent gastric distress such as cramping).